Studies will be undertaken to elucidate in early compensatory hypertrophy of the rodent kidney changes in RNA and protein metabolism that precede major increments in renal mass. Since the 20-40 percent increase in RNA per cell 2 days after contralateral nephrectomy does not appear to be a result of an increased rate of RNA synthesis, the possibility of increased post-transcriptional efficiency in the processing of nuclear precursor-ribosomal RNA will be investigated by comparing the ratios of methyl-labeled 28S and 18S RNA. While specific activities of amino-acid pools in kidney and plasma are determined and the kinetics of protein synthesis are being assessed, the role played by protein synthesis in the regulation of RNA metabolism will be studied; buoyant densities and labeling and electrophoretic characteristics of ribonucleoprotein particles and of their constituents will be measured. Searches for stimuli for compensatory hypertrophy will be narrowed by descriptions of parameters of growth produced by cross-circulation and by possible adsorption to polyethylene. Finally, a study will be made of a unique model of catabolic activity in kidney following discontinuance of a cross-circulation that previously was maintaining a state of compensatory hypertrophy. Clinical extensions of these data may provide a basis for quantitating and controlling growth in a diseased or transplanted kidney.